feat(ecosystem): add TickersFeed — pay-per-call stock data API via x402

[johnyi12]

Description

Adds TickersFeed to the x402 ecosystem directory.

TickersFeed is a pay-per-call US stock market data API built on x402. AI agents pay small amounts of USDC per request and receive stock data in return — no API keys, no subscriptions, no accounts required.

• Live on Base mainnet
• Endpoints: /stock/{symbol}, /crypto/{symbol}, /gas, /defi/yields, and more
• Catalog: https://api.tickersfeed.net/catalog
• Docs: https://tickersfeed.net

Tests

Checklist

• I have formatted and linted my code
• All new and existing tests pass
• My commits are signed (required for merge) -- you may need to rebase if you initially pushed unsigned commits
• I added a changelog fragment for user-facing changes (docs-only changes can skip)

[vercel]

@johnyi12 is attempting to deploy a commit to the Coinbase Team on Vercel.

A member of the Team first needs to authorize it.